The goal of this research is to investigate the maturation of procedural memory in the developing human brain. Procedural memory (skill learning or knowing how) is known to be dependent on the basal ganglia (BG), cerebellum, and related neocortices and is distinguished from declarative or explicit memory. Studies have begun to characterize the development of declarative memory, but very few have explored procedural memory. This is a major gap in knowledge, considering that procedural memory is a fundamental aspect of human cognition underlying many forms of learning that is moreover likely to be impaired in Attention- Deficit/hyperactivity Disorder (ADHD). In the current proposal, we aim to 1) characterize the development of procedural memory in typically developing children; 2) characterize the functional and structural maturation of the neural substrates important for procedural memory; and 3) characterize the development of procedural memory in children with ADHD. We propose to use variants of three classic procedural memory tasks for which there is strong neuropsychological evidence that they are isolated from declarative memory, which is known to change with development. These tasks moreover have distinct types of feedback: continuous visual feedback (closed-loop, associated with the cerebellum) and feedback in which there is a temporal gap between the mental/physical action and information about that action (open-loop, associated with the BG). We hypothesize three alternative outcomes: 1) Procedural memory will not change with age. 2) Like declarative memory, we will observe improvement with age through young adulthood; or 3) there will be a dissociation such that closed- loop learning will mature earlier than open-loop learning, reflecting the greater information processing demands of open-loop learning. If this ability is indeed compromised in ADHD, we expect worse performance in children with ADHD compared to age- and IQ-matched typically developing children. This should be especially true for BG-dependant tasks and when children with ADHD are not taking stimulant medication. 1) If procedural memory does not change with age, then neural recruitment should likewise not differ. However, previous work indicates that structural change of the BG is likely. To achieve adult levels of performance, despite immature BG, we would expect children to either a) recruit additional regions or b) recruit the BG to a greater extent. 2) If procedural memory abilities improve, we expect greater recruitment of the BG with age. 3) If we observe a dissociation, we expect a) functional recruitment for closed-loop forms of procedural memory (more dependant on the cerebellum) to change little with age and b) functional recruitment for open-loop forms (more dependent on the BG) to change with age. The proposed research would be the first to characterize the maturation of multiple forms of potentially dissociable kinds of procedural memory from young childhood to adulthood in typically developing children and those with ADHD.